function getDistance (lat1, lng1, lat2, lng2) {
    lat1 = lat1 || 0
    lng1 = lng1 || 0
    lat2 = lat2 || 0
    lng2 = lng2 || 0

    var rad1 = lat1 * Math.PI / 180.0
    var rad2 = lat2 * Math.PI / 180.0
    var a = rad1 - rad2
    var b = lng1 * Math.PI / 180.0 - lng2 * Math.PI / 180.0
    var r = 6378137
    var distance = r * 2 * Math.asin(Math.sqrt(Math.pow(Math.sin(a / 2), 2) + Math.cos(rad1) * Math.cos(rad2) * Math.pow(Math.sin(b / 2), 2)))

    return distance
}

module.exports = {
    getDistance
}